Polymers have in the past and continue to provide an attractive substitute for the more traditional types of structural materials (e.g. wood or metals) because of relatively inexpensive materials and fabrication cost. As polymers continue to find new applications in, for example, the fabrication of automotive parts and building materials, they must also become more durable and capable of withstanding prolonged exposure to a variety of degradative forces. Degradation of polymers can be caused by exposure to light, heat, moisture and/or air. Such degradation is usually manifest by either a partial or total loss of structural integrity, changes in light transmission properties, changes in color, loss or reduction of flexibility and/or resiliency, or any combination of the above phenomena. Those attempting to avoid polymer degradation have generally selected from among three possible approaches: (a) elimination or reduction of the degradative forces; (b) isolation of the sensitive material from the degradative forces; or (c) modification of the polymer composition to enhance its resistance to the degradative forces. The latter approach is generally preferable since it does not require elaborate engineering nor structural changes in the polymer product environment.
As one might readily expect, the problems associated with the stabilization of different polymeric materials are affected to a greater extent by the functionality of the polymer and any unsaturation that may be present along the backbone or the side chains of such materials. For example, where the polymer contains unsaturation along its backbone and/or side chains, it is highly sensitive to oxidative degradation. Materials that are suitable to prevent oxidative degradation of dienic or unsaturated polymers do not necessarily have similar beneficial effects when incorporated within a polymeric material lacking such unsaturation. Similarly, stabilizers which are effective for polyolefins, such as polyethylene, may have little, if any, stabilizing effect upon dienic polymers or polymers having unsaturation along their backbone or side chain.
There are a variety of additives which have been disclosed in the past as suitable for enhancing polymer resistance to one or more degradative forces described hereinabove. These additives (hereinafter collectively referred to as "stabilizers") can usually by physically combined with or engrafted on the environmentally sensitive polymer thereby prolonging its useful life in its hostile degradative environment. It is not uncommon for polymers to contain a variety of stabilizer materials, (i.e. a stabilizer package), each being present for prevention on a particular degradative reaction. One of the more difficult to control of the degradative forces is the irradiation of polymers by ultraviolet light. The impact of such irradiation will, of course, vary depending upon the intensity and duration of exposure and thus, may manifest itself only after a prolonged interval. The irradiation of polymers with ultraviolet light can often times cause crosslinking of these materials, thereby reducing its resiliency and/or impact resistance. Changes in color and opacity are often affected by prolonged exposure of polymers to UV irradiation. While many materials are known and commercially available as stabilizers against ultraviolet light degradation, the degree of protection afforded by such agents is generally concentration dependent and may be geared to a particular limited class of material.
The prior art is replete with technical articles and patents directed to resolving this complex problem; see, for example, "Photodegradation, Photooxidation and Photostabilization of Polymers", B. Ranby and J. Raybeck, John Wiley & Sons, New York, NY (1975). Hindered amines and phenols are commonly used AO/UV stabilizers for rubber and polymeric materials. Various amides have also been found useful as antioxidants.
U.S. Pat. No. 3,665,031 discloses antioxidants such as amides of phenol substituted acids which are produced by reacting acid derivatives with amino compounds. U.S. Pat. No. 3,780,103 teaches the preparation of alkylhydroxybenzylamides. Amino-acid amides are also disclosed in U.S. Pat. Nos. 2,153,707 and 3,247,200. U.S. Pat. No. 4,310,429 discloses substituted .alpha.-amino-acetamides as stabilizers for organic materials, the disclosure of which is herein incorporated by reference. Further, U.S. Pat. No. 3,960,984, which is incorporated by reference, discloses amide oligomers as heat stabilizers for oxymethylene polymers.
The present invention relates to novel oligomeric amides and their method of preparation. The novel oligomeric amides are useful as stabilizers for polymers, particularly as synergists for other AO/UV stabilizers. Thus, it is the object of this invention to provide a novel stabilizer material suitable for enhancing the resistance of polymers to oxidation and photodegradation. It is a further object of this invention to provide oligomeric stabilizers which are relatively non-volatile and resistant to extraction by solvents. It is yet another object of this invention to provide a method for preparation of novel oligomeric amide stabilizers in a one-step synthesis and with good yield.